Devices suitable for use in removing or installing modular electronic components from a substrate such as a printed circuit board generally fall into two categories, namely those which use a heated head which contacts each terminal to melt the solder, and those which use a blast of hot air to melt the solder. The former devices are generally very complex and employ a heated head having a plurality of spaced-apart fingers, each of which must be separately aligned with each terminal around the component to simultaneously heat the solder. The component is then withdrawn from the substrate by vacuum suction or other suitable mechanical means. The procedure is reversed for installing a component.
The latter devices direct a blast of hot air at the terminals from a source above the component to simultaneously melt the solder on each of the terminals. Examples of such devices are disclosed in U.S. Pat. Nos. 4,295,596 and 4,366,925. The devices in each of those two patents operate by directing a blast of hot air onto the terminals of a component, followed by removal of the component either mechanically or by the application of suction.
A disadvantage associated with the prior devices is that the heating source for the air is remote from the point at which the hot air is directed towards the terminals of the component, and as a result significant variations in temperature of the air are observed when the heater is turned on and air flows through the device ( the "run" time) and when the heater is turned off (the "idle" time) when air in the apparatus is permitted to cool down. As a result of this, when the heater is again switched on, there is a lag time during which the air is again raised to the solder melting temperature, and this results in increased energy consumption and time delay.
It is therefore a primary object of the present invention to provide an improved heating device suitable for use in the installation and removal of electronic components from circuits printed on a substrate.
It is another object of the present invention to provide a heating device which employs a heat exchange element for heating fluid, typically air, immediately prior to directing the heated air towards the terminals of the component on the substrate.
It is yet another object of the present invention to provide a heating device for directing heated air towards the plated-through holes remaining in a printed circuit board after removal of components from the board to melt and remove solder remainining in the holes.
It is a yet further object of the present invention to provide a heating device utilizing a heat conductive foil as a heat exchange element.
It is a further object of the present invention to provide a heating device suitable for heating a substrate on the side opposite to that which is being heated (to facilitate attachment or removal of components from the board), to reduce thermal shock and preheat the substrate.